Thermodynamics



Thermodynamics (from the Greek θερμη, therme, meaning "efficiency of early steam engines.[3]   The starting point for most thermodynamic considerations are the spontaneous processes.

With these tools, thermodynamics describes how systems respond to changes in their surroundings. This can be applied to a wide variety of topics in science and engineering, such as engines, materials science to name a few.[6][7]

History

 

Main article: History of thermodynamics

A brief history of thermodynamics begins with Otto von Guericke who in 1650 built and designed the world's first bone digester, which was a closed vessel with a tightly fitting lid that confined steam until a high pressure was generated.

Later designs implemented a steam release valve that kept the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and a cylinder engine. He did not, however, follow through with his design. Nevertheless, in 1697, based on Papin's designs, engineer Thomas Savery built the first engine. Although these early engines were crude and inefficient, they attracted the attention of the leading scientists of the time. One such scientist was Motive power. This marks the start of thermodynamics as a modern science.[1]

The term thermodynamics was coined by William Rankine, originally trained as a physicist and a civil and mechanical engineering professor at the University of Glasgow.[10]

Classical thermodynamics

Main article: Classical thermodynamics

Classical thermodynamics is the original early 1800s variation of thermodynamics concerned with thermodynamic states, and properties as energy, work, and heat, and with the laws of thermodynamics, all lacking an atomic interpretation. In precursory form, classical thermodynamics derives from chemist William Thomson (Lord Kelvin).

Statistical thermodynamics

Main article: Statistical thermodynamics

With the development of atomic and molecular theories in the late 1800s and early 1900s, thermodynamics was given a molecular interpretation. This field is called statistical thermodynamics, which can be thought of as a bridge between macroscopic and microscopic properties of systems. Essentially, statistical thermodynamics is an approach to thermodynamics situated upon phenomenological thermodynamics, which gives scientific descriptions of phenomena with avoidance of microscopic details. The statistical approach is to derive all macroscopic properties (temperature, volume, pressure, energy, entropy, etc.) from the properties of moving constituent particles and the interactions between them (including quantum phenomena). It was found to be very successful and thus is commonly used.


Chemical thermodynamics

Main article: Chemical thermodynamics

Chemical thermodynamics is the study of the interrelation of E. A. Guggenheim began to apply the mathematical methods of Gibbs to the analysis of chemical processes.[12]

Thermodynamic systems

Main article: Thermodynamic system

  An important concept in thermodynamics is the “system”. Everything in the universe except the system is known as surroundings. A system is the region of the universe under study. A system is separated from the remainder of the universe by a heat, or matter between the system and the surroundings take place across this boundary. Boundaries are of four types: fixed, moveable, real, and imaginary.

Basically, the “boundary” is simply an imaginary dotted line drawn around the volume of a something in which there is going to be a change in the quantum thermodynamics.

For an engine, a fixed boundary means the piston is locked at its position; as such, a constant volume process occurs. In that same engine, a moveable boundary allows the piston to move in and out. For closed systems, boundaries are real while for open system boundaries are often imaginary. There are five dominant classes of systems:

  1. Isolated Systems – matter and energy may not cross the boundary.
  2. Adiabatic Systems – heat must not cross the boundary.
  3. Diathermic Systems - heat may cross boundary.
  4. Closed Systems – matter may not cross the boundary.
  5. Open Systems – heat, work, and matter may cross the boundary (often called a control volume in this case).

As time passes in an isolated system, internal differences in the system tend to even out and pressures and temperatures tend to equalize, as do density differences. A system in which all equalizing processes have gone practically to completion, is considered to be in a thermodynamic equilibrium.

In thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems which are not in equilibrium. Often, when analysing a thermodynamic process, it can be assumed that each intermediate state in the process is at equilibrium. This will also considerably simplify the situation. Thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state are said to be reversible processes.

Thermodynamic parameters

Main article: Conjugate variables (thermodynamics)

The central concept of thermodynamics is that of energy, the ability to do work. As stipulated by the conjugate variables. The most common conjugate thermodynamic variables are pressure-volume (mechanical parameters), temperature-entropy (thermal parameters), and chemical potential-particle number (material parameters).

Thermodynamic instruments

Main article: Thermodynamic instruments

There are two types of thermodynamic instruments, the meter and the reservoir. A thermodynamic meter is any device which measures any parameter of a ideal gas law PV=nRT, the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device, called a barometer may also be constructed from a sample of an ideal gas held at a constant temperature. A calorimeter is a device which is used to measure and define the internal energy of a system.

A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. The earth's atmosphere is often used as a pressure reservoir.

It is important that these two types of instruments are distinct. A meter does not perform its task accurately if it behaves like a reservoir of the state variable it is trying to measure. If, for example, a thermometer, were to act as a temperature reservoir it would alter the temperature of the system being measured, and the reading would be incorrect. Ideal meters have no effect on the state variables of the system they are measuring.

Thermodynamic states

Main article: Thermodynamic state

When a system is at equilibrium under a given set of conditions, it is said to be in a definite state. The state of the system can be described by a number of intensive variables and extensive variables. The properties of the system can be described by an equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant

Thermodynamic processes

Main article: Thermodynamic processes

A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. Furthermore, it is useful to group these processes into pairs, in which each variable held constant is one member of a conjugate pair. The seven most common thermodynamic processes are shown below:

  1. An isobaric process occurs at constant pressure.
  2. An isochoric process, or isometric/isovolumetric process, occurs at constant volume.
  3. An isothermal process occurs at a constant temperature.
  4. An adiabatic process occurs without loss or gain of heat.
  5. An isentropic process (reversible adiabatic process) occurs at a constant entropy.
  6. An isenthalpic process occurs at a constant enthalpy.
  7. A steady state process occurs without a change in the internal energy of a system.

The laws of thermodynamics

Main article: Laws of thermodynamics

In thermodynamics, there are four laws of very general validity, and as such they do not depend on the details of the interactions or the systems being studied. Hence, they can be applied to systems about which one knows nothing other than the balance of energy and matter transfer. Examples of this include Einstein's prediction of spontaneous emission around the turn of the 20th century and current research into the thermodynamics of black holes.

The four laws are:

If two thermodynamic systems are separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other.
The change in the work done on the system.
The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value.
As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value; also stated as: "the entropy of all systems and of all states of a system is zero at absolute zero" or equivalently "it is impossible to reach the absolute zero of temperature by any finite number of processes".
See also: negative temperature.

Thermodynamic potentials

Main article: Thermodynamic potentials

As can be derived from the energy balance equation on a thermodynamic system there exist energetic quantities called thermodynamic potentials, being the quantitative measure of the stored energy in the system. The five most well known potentials are:

Internal energy U\,
Helmholtz free energy A=U-TS\,
Enthalpy H=U+PV\,
Gibbs free energy G=U+PV-TS\,
Grand potential \Phi_{G}=U-TS-\mu N\,

Other thermodynamic potentials can be obtained through Legendre transformations. Potentials are used to measure energy changes in systems as they evolve from an initial state to a final state. The potential used depends on the constraints of the system, such as constant temperature or pressure. Internal energy is the internal energy of the system, enthalpy is the internal energy of the system plus the energy related to pressure-volume work, and Helmholtz and Gibbs energy are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.

Quotes & humor

Wikiquote has a collection of quotations related to:
Transwiki:Quotes & humor (thermodynamics)
  • Attributed to Arnold Sommerfeld:
“ Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, it doesn't bother you any more. ”

See also

Physics Portal

Related branches

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Wikibooks

  • Engineering Thermodynamics
  • Entropy for Beginners

References

  1. ^ a b c Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6. 
  2. ^ Clark, John, O.E. (2004). The Essential Dictionary of Science. Barnes & Noble Books. ISBN 0-7607-4616-8. 
  3. ^ Clausius, Rudolf (1850). On the Motive Power of Heat, and on the Laws which can be deduced from it for the Theory of Heat. Poggendorff's Annalen der Physick, LXXIX (Dover Reprint). ISBN 0-486-59065-8. 
  4. ^ Van Ness, H.C. (1969). Understanding Thermodynamics. Dover Publications, Inc.. ISBN 0-486-63277-6. 
  5. ^ Dugdale, J.S. (1998). Entropy and its Physical Meaning. Taylor and Francis. ISBN 0-7484-0569-0. 
  6. ^ Smith, J.M.; Van Ness, H.C., Abbott, M.M. (2005). Introduction to Chemical Engineering Thermodynamics. McGraw Hill. ISBN 0-07-310445-0. 
  7. ^ Haynie, Donald, T. (2001). Biological Thermodynamics. Cambridge University Press. ISBN 0-521-79549-4. 
  8. ^ Partington, J.R. (1989). A Short History of Chemistry. Dover. ISBN 0-486-65977-1. 
  9. ^ Kelvin, William T. (1849) "An Account of Carnot's Theory of the Motive Power of Heat - with Numerical Results Deduced from Regnault's Experiments on Steam." Transactions of the Edinburg Royal Society, XVI. January 2. Scanned Copy
  10. ^ Cengel, Yunus A.; Boles, Michael A. (2005). Thermodynamics - An Engineering Approach. McGraw-Hill. ISBN 0-07-310768-9. 
  11. ^ Gibbs, Willard (1993). The Scientific Papers of J. Willard Gibbs, Volume One: Thermodynamics. Ox Bow Press. ISBN 0-918024-77-3. 
  12. ^ Lewis, Gilbert N.; Randall, Merle (1923). Thermodynamics and the Free Energy of Chemical Substances. McGraw-Hill Book Co. Inc.. 

Further reading

  • Cengel, Yunus A.; Boles, Michael A. (2002). Thermodynamics - An Engineering Approach. McGraw Hill. ISBN 0-07-238332-1. 
  • Kroemer, Herbert; Kittel, Charles (1980). Thermal Physics. W. H. Freeman Company. ISBN 0-7167-1088-9. 
  • Goldstein, Martin; Inge, F (1993). The Refrigerator and the Universe. Harvard University Press. ISBN 0-674-75325-9. 
  • Dunning-Davies, Jeremy (1997). Concise Thermodynamics: Principles and Applications. Horwood Publishing. ISBN 1-8985-6315-2. 
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Thermodynamics". A list of authors is available in Wikipedia.